Aircraft landing gear provided with a leaf spring locking device

ABSTRACT

An aircraft undercarriage comprising: a leg connected to an aircraft structure to be movable between a deployed position and a retracted position; a brace member for holding the leg in its deployed position and comprising a first rod hinged to the aircraft structure and a second rod hinged to the first link and to the leg; a stabilizer member for holding the first and second rods in an aligned position and comprising a first link and a second link that are hinged to each other, with at least one of them being hinged to the brace member; and a spring for elastically urging the hinges of the first and second links into a generally aligned position. 
     The spring comprises at least one spring blade arranged to be subjected to an axial compression force when the first and second links leave the generally aligned position.

The present invention relates to the field of landing gear, and moreparticularly to means for enabling an undercarriage to be locked in itsdeployed position.

BACKGROUND OF THE INVENTION

Aircraft undercarriages are known that comprise a leg connected to thestructure of an aircraft so as to be movable, under the action of adrive actuator, between a deployed position (for takeoff and landing)and a retracted position (in flight).

The leg is held in the deployed position by a breakable strut that iscoupled both to the leg and to the structure of the aircraft, and thatcomprises two rods that are hinged together and held in an alignedposition by a stabilizer member.

The stabilizer member comprises two links that are hinged together andheld in a substantially aligned position by a passive locking member inorder to prevent the strut from coming out of alignment.

In general, the locking member comprises one or more coil springs havingends connected to the strut and to the stabilizer member so as to exerta traction force on said stabilizer member and thus prevent the linksfrom coming out of alignment.

It is common practice for the undercarriage to be arranged so that, inthe event of the drive actuator failing, it can be moved under gravityfrom its retracted position to its deployed position. The coil springsare generally designed to assist in moving the undercarriage to itsdeployed position and to lock it in that position.

As a result, the coil springs oppose the action of the drive actuatorwhile the undercarriage is being raised, and the linear behavior of thecoil springs gives rise to large additional forces that need to beovercome while the undercarriage is being moved to its retractedposition, and the drive actuator must be designed accordingly.

Furthermore, coil springs are expensive and relatively heavy.

OBJECT OF THE INVENTION

An object of the invention is thus to propose an aircraft undercarriageenabling the above-mentioned problems to be obviated at least in part.

SUMMARY OF THE INVENTION

To this end, the invention provides an aircraft undercarriagecomprising:

-   -   a leg arranged to be connected to an aircraft structure to be        movable between a deployed position and a retracted position;    -   at least one brace member for holding the leg in its deployed        position and comprising a first rod hinged to the aircraft        structure and a second rod hinged to the first rod and to the        leg;    -   a stabilizer member for holding the first and second rods in an        aligned position and comprising a first link and a second link        that are hinged to each other, with at least one of them being        hinged to the brace member; and    -   at least one spring for elastically urging the hinges of the        first and second links into a generally aligned position.

According to the invention, the spring is a spring blade arranged to besubjected elastically to an axial compression force when the hinges ofthe first and second links leave their generally aligned position.

Compressing the blade axially causes it to buckle in such a manner thatthe force that needs to be delivered for breaking the alignment of thelinks varies little while the blade is buckling. While the undercarriageis being deployed, this behavior of the spring blade makes it possibleto obtain a force that is sufficient for locking the undercarriage inits deployed position at the end of a stroke that is small, and whilethe undercarriage is being raised, this behavior limits the forces thatneed to be overcome by the drive actuator.

Furthermore, such a locking member is found to be inexpensive to produceand it is relatively light in weight.

In particular manner, the spring blade is pivotally connected to thefirst rod and to the stabilizer member.

In particular manner, the spring blade is pivotally connected to thesecond rod and to the stabilizer member.

According to a particular characteristic, the spring blade is a metalplate of substantially constant thickness.

According to another particular characteristic, the undercarriageincludes two spring blades in order to provide redundancy in the eventof one of the two spring blades failing.

In particular manner, the two spring blades are substantially identicaland they are pivotally connected to the first rod and to the stabilizermember.

In particular manner, the two spring blades are substantially identicaland they are pivotally connected to the second rod and to the stabilizermember.

In particular manner, one of the spring blades is pivotally connected tothe first rod and to the stabilizer member, and the other spring bladeis pivotally connected to the second rod and to the stabilizer member.

In particular manner, the first link is hinged to the leg and the secondlink is hinged to the brace member.

In particular manner, the first link is hinged to the second rod and thesecond link is hinged to the first rod.

The invention also provides an aircraft including at least one suchundercarriage.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood in the light of the followingdescription, which is purely illustrative and nonlimiting, and whichshould be read with reference to the accompanying drawings, in which:

FIG. 1 a is a diagrammatic view of an aircraft undercarriage in a firstembodiment of the invention, shown in its deployed position;

FIG. 1 b is is a view analogous to Figure la, showing the undercarriagein an unlocked position;

FIG. 1 c is is a view analogous to Figure la, showing the undercarriagein an intermediate position at the beginning of the raising stage;

FIG. 2 is a graph plotting the compression force produced by the springblade as a function of its movement;

FIG. 3 is a view analogous to FIG. 1 showing an aircraft undercarriagein a second embodiment of the invention;

FIG. 4 is a view analogous to FIG. 1 showing an aircraft undercarriagein a third embodiment of the invention;

FIG. 5 is is a perspective view of a portion of an undercarriage in afourth embodiment of the invention; and

FIG. 6 is is a diagrammatic view of the locking member of theundercarriage shown in FIG. 5 .

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 1 a to 1 d , an aircraft undercarriage 1comprises, in conventional manner, a leg 2 having a first end hinged toa structure 3 of an aircraft about a hinge axis X1 so that the leg 2 ismovable between a deployed position (FIG 1 a ) and a retracted positionunder the action of a drive actuator (not shown), e.g. a hydraulicactuator. The leg 2 has an opposite end (not shown in the figures)carrying an axle having one or more wheels rotatably mounted thereon.

A breakable strut 4 is hinged firstly to the leg 2 and secondly to thestructure 3 of the aircraft, and it forms a brace member for holding theleg 2 in its deployed position. The breakable strut 4 comprises two rods4 a and 4 b that are hinged together about a hinge axis X2 at a knee 4c. The rod 4 a is also hinged to the structure 3 of the aircraft about ahinge axis X3, while the rod 4 b is hinged to the leg 2 about a hingeaxis X4.

The breakable strut 4 is stabilized in a substantially aligned positionby means of a stabilizer member 5 comprising two links 5 a and 5 b thatare also hinged together about a hinge axis X5 at a knee 5 c. The link 5a is hinged to the leg 2 about a hinge axis X6, and the link 5 b ishinged to the breakable strut 4 about the axis X2. The links 5 a and 5 bare held in a substantially aligned position by a locking member 6urging the links 5 a and 5 b towards the locked position as shown inFIG. 1 a and as defined by abutments between the links 5 a and 5 b.

When it is thus stabilized in a substantially aligned position, thefoldable strut 2 opposes any pivoting of the leg 4 about its hinge axisX1, such that the deployed position shown in FIG. 1 a is a stableposition. As is well known, the rods 4 a and 4 b and the links 5 a and 5b are designed so that in order to reach the locked position shown inFIG. 1 , both the hinge knee 4 c between the rods 4 a and 4 b and alsothe hinge knee 5 c between the links 5 a and 5 b go a little way beyondthe rods 4 a and 4 b and the links 5 a and 5 b being in geometricalalignment. In known manner, the hinges are arranged to avoid becomingstatically indeterminate, e.g. by means of operating clearances or atleast one ball joint.

The locking member 6 comprises a spring for holding the links 5 a and 5b elastically in the substantially aligned position. In accordance withthe invention, in this embodiment, the spring is a metal blade 7 ofelongate shape that extends along the rod 4 a. The blade 7 presentsthickness and width that are generally constant, with its width beingtaken as extending substantially parallel to the hinge axes X1-X6 andbeing greater than its thickness. For example, the blade 7 may have alength equal to 800 millimeters (mm), a thickness equal to 50 mm, and athickness equal to 3.5 mm. The blade 7 has a first end 7.1 pivotallyconnected to the rod 4 a to pivot about a pivot axis X7 situated in theproximity of the hinge axis X3 of the rod 4 a, and a second end 7.2pivotally connected to the stabilizer member 5 to pivot about a pivotaxis X8 in the proximity of the hinge axis X2 of the knee 4 c. Thus,when the leg 2 is in its deployed position, the blade 7 is in a deformedstate close to its rest state with the end 7.1 being spaced apart fromthe end 7.2 by a first distance; when the leg 2 is in its retractedposition, the blade 7 has buckled and is in a deformed state with theend 7.1 being spaced apart from the end 7.2 by a second distance that isless than the first distance. It is the folding of the locking member 6that causes the ends 7.1 and 7.2 to move towards each other and thuscauses the blade 7 to buckle. The blade 7 is thus stressed elasticallyin compression, and it tends to return towards its rest state, with theends 7.1 and 7.2 tending to move apart from each other back towards thefirst distance.

For this purpose, the blade 7 is substantially straight when the links 5a and 5 b are in the locked position (FIG. 1 a ), and it takes on anarcuate shape when the link 5 b pivots about the axis X2 (FIGS. 1 b and1 c ).

The blade 7 thus forms a spring blade applying a force P on the link 5 bfor bringing the links 5 a and 5 b into the substantially alignedposition.

With reference to Figures lb and lc, the drive actuator is designed tobreak the alignment of the links 5 a and 5 b by overcoming the force Pexerted by the blade 7 opposing its own buckling. Raising the knee 5 cbrings the rods 4 a and 4 b out of alignment, thereby raising the knee 4c and thus causing the leg 2 to pivot towards its retracted position(FIGS. 1 b and 1 c ).

As shown in FIG. 2 , the force P delivered by the blade 7 after beingdeformed by a small amount U is sufficient to keep the links 5 a and 5 bin the locked position. Furthermore, the force P varies very little whenthe deformation U is increased, in particular in comparison with thelinear behavior of coil springs. Thus, when the leg 2 goes from itsdeployed position to its retracted position, the force P produced by theblade 7 is limited, thereby limiting the forces that need to be overcomeby the drive actuator in order to raise the undercarriage 1.Furthermore, the spring formed by the blade 7 is less expensive andsomewhat lighter.

It should be observed that the blade 7 needs to be positioned on thebreakable strut 4 in a manner that is different from the positioning ofcoil springs, since the blade 7 is arranged to operate exclusively incompression and not frequently in traction.

The main parameters needed for designing the blade 7 are:

-   -   the force needed for holding the links 5 a and 5 b in their        substantially aligned position;    -   the mechanical characteristics of the material from which the        blade 7 is made (conventional elastic limit Rp0.2, Young's        modulus E, fatigue curve, . . . );    -   the maximum deformation of the blade 7 during deployment and        retraction of the leg 2, in particular for guaranteeing the        mechanical strength of said blade 7; and    -   the maximum buckling of the blade during deployment and        retraction of the leg 2, in particular in order to limit the        space occupied by the blade 7 throughout the        retraction/extension movement of the leg 2.

FIG. 5 shows another embodiment of the invention, in which theundercarriage 1 includes a stabilizer member that is said to be mounted“internally” in order to hold the first and 2nd rods 4 a and 4 b in thealigned position. The stabilizer member 5′ comprises two links 5 a′ and5 b′ that are hinged together about a hinge axis X5′ at a knee 5 c′. Thelink 5 a′ is hinged to the rod 4 b about an axis X2′, and the link 5 b′is hinged to the rod 4 a about a hinge axis X6′. The hinge axes X2′,X5′, and X6′ of the links 5 a′ and 5 b′ are held in a substantiallyaligned position by a locking member 6′ urging the links 5 a′ and 5 b′towards the locked position as shown in

FIG. 6 and as defined by an abutment 5 d′ between the links 5 a′ and 5b′.

When it is thus stabilized in a substantially aligned position, thebreakable strut 4 opposes any pivoting of the leg 2 about its hinge axisX1. As is well known, the links 5 a′ and 5 b′ are designed in such amanner as to reach the locked position shown in FIG. 6 after the hingeaxis X2′ of the link 5 a′ has gone a little beyond the hinge axes X2′,X5′, and X6′ being geometrically in alignment. In known manner, thehinges are arranged to avoid becoming statically indeterminate, e.g. bymeans of operating clearances or at least one ball joint.

With reference to FIG. 5 , the locking member 6′ includes a spring forholding the hinge axes X2′, X5′, and X6′ of the links 5 a′ and 5 b′elastically in the substantially aligned position. In this embodiment,the spring comprises two metal blades 7′ of elongate shape that extendparallel to each other along the rod 4 a. The blades 7′ are identicaland present thickness and width that are generally constant, with theirwidth being taken as extending substantially parallel to the hinge axesX1-X4 and being greater than their thickness.

The blades 7′ have first ends 7.1′ pivotally connected to the rod 4 a topivot about a common pivot axis X7′ situated in the proximity of thehinge axis X3 of the rod 4 a, and second ends 7.2′ pivotally connectedto the link 5 b′ to pivot about a common pivot axis X8′ in the proximityof the hinge axis X2 of the knee 4 c. Thus, when the leg 2 is in itsdeployed position, the blades 7′ are in a deformed state close to theirrest state and the ends 7.1′ are spaced apart from the ends 7.2′ by afirst distance; when the leg 2 is in its retracted position, the blades7′ have buckled and are in a deformed state with the ends 7.1′ beingspaced apart from the ends 7.2′ by a second distance that is less thanthe first distance. It is the folding of the locking member 6′ thatcauses the ends 7.1′ and 7.2′ to move towards each other and thus causesthe blades 7′ to buckle. The blade 7′ are thus stressed elastically incompression, and they tend to return towards their rest state, with theends 7.1′ and 7.2′ tending to move apart from each other back towardsthe first distance.

For this purpose, each of the first and second ends 7.1′ and 7.2′ ofeach of the blades 7′ is riveted to a fitting 8 that is arranged to bepivotally connected to a tongue 9.1 fastened to the rod 4 a or to atongue 9.2 integral with the link 5 a′ in such a manner that the blades7′ are substantially straight when the links 5 a′ and 5 b′ are in thelocked position (FIGS. 5 and 6 ), and can take up an arcuate shape whenthe link 5 b′ pivots about the axis X6′.

Each of the blades 7′ thus forms a spring blade applying a force to thelink 5 b′ for bringing the hinge axes X2′, X5′, and X6′ into asubstantially aligned position. The presence of two blades 7′ serves inparticular to provide redundancy in the event of one of the two blades7′ failing.

The drive actuator is designed to break the alignment of the hinge axesX2′, X5′, and X6′ by overcoming the force exerted by the blades 7′opposing their own buckling. Raising the knee 5 c′ brings the rods 4 aand 4 b out of alignment, thereby raising the knee 4 c and thus causingthe leg 2 to pivot towards its retracted position.

The force delivered by the blades 7′ after being deformed by a smallamount is sufficient to keep the links 5 a′ and 5 b′ in the lockedposition. The force varies very little with increasing deformation.Thus, when the leg 2 goes from its deployed position to its retractedposition, the force produced by the blades 7′ is limited, therebylimiting the forces that needed to be overcome by the drive actuator inorder to raise the undercarriage 1.

Naturally, the invention is not limited to the embodiment described, butcovers any variant coming within the ambit of the invention as definedby the claims. he number, the shapes and the dimensions of the blades 7,7′ need not be the same as shown in FIGS. 1 a-1 d , and 5.

Although above, the blades 7, 7′ extend along the rod 4 a (so-called“internal” mounting), they could 30 equally well extend along the rod 4b (so-called “external” mounting). The blades 7, 7′ are then pivotallyconnected to the stabilizer member 5, 5′ and to the rod 4 b so as to bestressed in compression (FIG. 3 ).

The leg 2 may equally well be stabilized by combining the action of oneor more pivotally-mounted blades extending along the rod 4 a with theaction of one or more pivotally-mounted blades extending along the rod 4b (FIG. 4 ).

The blades 7, 7′ may be made out of any suitable material (metal,composite, . . . ). The blades 7, 7′ may be pivotally connected to therods 4 a and 4 b and on the stabilizer member 5, 5′ by any appropriatemeans.

Although above the leg 2 is held in the deployed position by a singlebreakable strut 4, the invention also applies equally to undercarriagescomprising a leg that is held in the deployed position by a plurality ofbreakable struts. At least one of the breakable struts would then befitted with a stabilizer member including at least one spring blade.

1. An aircraft undercarriage comprising: a leg arranged to be connectedto an aircraft structure to be movable between a deployed position and aretracted position; at least one brace member for holding the leg in itsa deployed position and comprising a first rod hinged to the aircraftstructure and a second rod hinged to the first rod and to the leg; astabilizer member for holding the first rod and the second rodrods in analigned position and comprising a first link and a second link that arehinged to each other, with at least one of the first link and the secondlink being hinged to the at least one brace member; and at least onespring for elastically urging the hinges of the first link and thesecond link into an aligned position; wherein the at least one spring isa spring blade arranged to be subjected elastically to an axialcompression force when the hinges of the first link and the second linkleave the aligned position.
 2. The aircraft undercarriage according toclaim 1, wherein the spring blade is pivotally connected to the firstrod and to the stabilizer member.
 3. The aircraft undercarriageaccording to claim 1, wherein the spring blade is pivotally connected tothe second rod and to the stabilizer member.
 4. The aircraftundercarriage according to claim 1, wherein the spring blade is a metalplate of substantially constant thickness.
 5. The aircraft undercarriageaccording to claim 1, wherein the spring blade comprises two springblades in order to provide redundancy in the event of one of the twospring blades fails.
 6. The aircraft undercarriage according to claim 5,wherein the two spring blades are substantially identical and arepivotally connected to the first rod and to the stabilizer member. 7.The aircraft undercarriage according to claim 5, wherein the two springblades are substantially identical and mare pivotally connected to thesecond rod and to the stabilizer member.
 8. The aircraft undercarriageaccording to claim 5, wherein one of the two spring blades is pivotallyconnected to the first rod and to the stabilizer member, and the otherof the two spring blades is pivotally connected to the second rod and tothe stabilizer member.
 9. The aircraft undercarriage according to claim1, wherein the first link is hinged to the leg and the second link ishinged to the at least one brace member.
 10. The aircraft undercarriageaccording to claim 1, wherein the first link is hinged to the second rodand the second link is hinged to the first rod.
 11. An aircraftincluding at least one aircraft undercarriage according to claim 1.